1. Technical Field
The present invention relates to a virtual image display apparatus that presents a viewer with video images in the form of virtual images, and particularly to an optical member suitable for a head-mounted display worn around the head of the viewer and a virtual image display apparatus using the optical member.
2. Related Art
A variety of optical systems incorporated in a virtual image display apparatus, such as a head-mounted display (hereinafter also referred to as HMD) worn around the head of a viewer, have been proposed. In particular, a variety of optical prisms used in front of the eyes have also been proposed (see JP-A-11-149003 and JP-A-10-268114, for example).
A virtual image display apparatus, such as an HMD, is desired to achieve further size and weight reduction and an increase in the angle of view without degradation in image quality. Further, when the entire view of the viewer is covered and only video image light is visible to the viewer, the viewer is unable to know what is going on outside and hence feels anxious. Instead, when the viewer is allowed to see the outside superimposed with video images, a new application, such as virtual reality, is created. It is therefore desired to develop a display that does not obstruct the outside view but displays it with video image light superimposed thereon.
In view of the circumstances described above, it is conceivable to configure a virtual image display apparatus based, for example, on a prism-shaped optical member having a plurality of free-form surfaces and so disposed in front of the viewer's eyes that see-through observation is achieved and guide video image light from an image display device to the viewer's eyes via the see-through-type optical member. In a virtual image display apparatus of this type, in particular, to improve comfort and appearance of the viewer who wears the virtual image display apparatus, it is typically desirable that the shape of the apparatus is similar to that of glasses. To make the shape of the virtual image display apparatus similar to that of glasses, among parts that form the virtual image display apparatus, the shape of a light guide portion disposed in front of each eye is particularly important.
On the other hand, it is also an important precondition that an optical member that forms the light guide portion has a light guiding function. When the optical member has a complicated shape, such as a shape including free-form surfaces, it is important to ensure assembly precision in order to maintain, for example, high-precision image quality.